Supplemental Oil and Gas Information (Costs Incurred in Oil and Gas Property Acquisition, Exploration and Development Activities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Property acquisition costs
Unproved	$ 92.9		$ 35.6		$ 132.5
Proved	7.4		13.2		311.5
Total acquisition costs	100.3		48.8		444.0
Exploration costs	430.1	[1]	493.7	[1]	448.0	[1]
Development costs	3,282.7	[1]	3,939.6	[1]	3,521.7	[1]
Total Costs	3,813.1		4,482.1		4,413.7
Charged to expense
Dry hole expense	270.0		262.9		181.1
Geophysical and other costs	169.2		172.4		69.0
Total charged to expense	439.2		435.3		250.1
Property additions	3,373.9		4,046.8		4,163.6
Exploration costs	430.1	[1]	493.7	[1]	448.0	[1]
Development costs	3,282.7	[1]	3,939.6	[1]	3,521.7	[1]
Total Costs	3,813.1		4,482.1		4,413.7
United States [Member]
Property acquisition costs
Unproved	92.9		32.4		107.7
Proved	7.4		13.2		69.1
Total acquisition costs	100.3		45.6		176.8
Exploration costs	160.0	[1]	112.4	[1]	174.5	[1]
Development costs	1,934.7	[1]	1,773.2	[1]	1,352.7	[1]
Total Costs	2,195.0		1,931.2		1,704.0
Charged to expense
Dry hole expense	92.1		46.1		32.3
Geophysical and other costs	37.7		29.1		19.6
Total charged to expense	129.8		75.2		51.9
Property additions	2,065.2		1,856.0		1,652.1
Exploration costs	160.0	[1]	112.4	[1]	174.5	[1]
Development costs	1,934.7	[1]	1,773.2	[1]	1,352.7	[1]
Total Costs	2,195.0		1,931.2		1,704.0
Canada [Member]
Property acquisition costs
Unproved					14.6
Proved					242.4
Total acquisition costs					257.0
Exploration costs	1.7	[1]	21.8	[1]	57.0	[1]
Development costs	413.8	[1]	351.6	[1]	664.5	[1]
Total Costs	415.5		373.4		978.5
Charged to expense
Dry hole expense			32.1		8.0
Geophysical and other costs	1.7		0.7		2.5
Total charged to expense	1.7		32.8		10.5
Property additions	413.8		340.6		968.0
Exploration costs	1.7	[1]	21.8	[1]	57.0	[1]
Development costs	413.8	[1]	351.6	[1]	664.5	[1]
Total Costs	415.5		373.4		978.5
Malaysia [Member]
Property acquisition costs
Exploration costs	6.3	[1]	14.9	[1]	68.8	[1]
Development costs	926.6	[1]	1,787.7	[1],[2]	1,433.7	[1]
Total Costs	932.9		1,802.6		1,502.5
Charged to expense
Dry hole expense	47.4		20.7		26.1
Geophysical and other costs	1.3		4.6		1.1
Total charged to expense	48.7		25.3		27.2
Property additions	884.2		1,777.3		1,475.3
Exploration costs	6.3	[1]	14.9	[1]	68.8	[1]
Development costs	926.6	[1]	1,787.7	[1],[2]	1,433.7	[1]
Total Costs	932.9		1,802.6		1,502.5
Non-cash capital lease obligation			358.0
United Kingdom [Member]
Property acquisition costs
Exploration costs					(1.0)	[1],[3]
Development costs			8.1	[1],[3]	46.6	[1],[3]
Total Costs			8.1	[3]	45.6	[3]
Charged to expense
Dry hole expense					(0.8)	[3]
Geophysical and other costs					(0.2)	[3]
Total charged to expense					(1.0)	[3]
Property additions			8.1	[3]	46.6	[3]
Exploration costs					(1.0)	[1],[3]
Development costs			8.1	[1],[3]	46.6	[1],[3]
Total Costs			8.1	[3]	45.6	[3]
Other Regions [Member]
Property acquisition costs
Unproved			3.2	[4]	10.2	[4]
Total acquisition costs			3.2	[4]	10.2	[4]
Exploration costs	262.1	[1],[4]	344.6	[1],[4]	148.7	[1],[4]
Development costs	7.6	[1],[4]	19.0	[1],[4]	24.2	[1],[4]
Total Costs	269.7	[4]	366.8	[4]	183.1	[4]
Charged to expense
Dry hole expense	130.5	[4]	164.0	[4]	115.5	[4]
Geophysical and other costs	128.5	[4]	138.0	[4]	46.0	[4]
Total charged to expense	259.0	[4]	302.0	[4]	161.5	[4]
Property additions	10.7	[4]	64.8	[4]	21.6	[4]
Exploration costs	262.1	[1],[4]	344.6	[1],[4]	148.7	[1],[4]
Development costs	7.6	[1],[4]	19.0	[1],[4]	24.2	[1],[4]
Total Costs	269.7	[4]	366.8	[4]	183.1	[4]
Asset Retirement Obligation Costs [Member]
Property acquisition costs
Exploration costs			0.2		(1.6)
Development costs	70.6		171.9		173.3
Total Costs	70.6		172.1		171.7
Charged to expense
Exploration costs			0.2		(1.6)
Development costs	70.6		171.9		173.3
Total Costs	70.6		172.1		171.7
Asset Retirement Obligation Costs [Member] | United States [Member]
Property acquisition costs
Exploration costs					(1.7)
Development costs	36.5		70.1		37.9
Total Costs	36.5		70.1		36.2
Charged to expense
Exploration costs					(1.7)
Development costs	36.5		70.1		37.9
Total Costs	36.5		70.1		36.2
Asset Retirement Obligation Costs [Member] | Canada [Member]
Property acquisition costs
Exploration costs			0.2		0.1
Development costs	(32.1)		5.9		80.7
Total Costs	(32.1)		6.1		80.8
Charged to expense
Exploration costs			0.2		0.1
Development costs	(32.1)		5.9		80.7
Total Costs	(32.1)		6.1		80.8
Asset Retirement Obligation Costs [Member] | Malaysia [Member]
Property acquisition costs
Development costs	66.2		95.9		48.6
Total Costs	66.2		95.9		48.6
Charged to expense
Development costs	66.2		95.9		48.6
Total Costs	66.2		95.9		48.6
Asset Retirement Obligation Costs [Member] | United Kingdom [Member]
Property acquisition costs
Development costs					(11.5)
Total Costs					(11.5)
Charged to expense
Development costs					(11.5)
Total Costs					(11.5)
Asset Retirement Obligation Costs [Member] | Other Regions [Member]
Property acquisition costs
Development costs					17.6
Total Costs					17.6
Charged to expense
Development costs					17.6
Total Costs					$ 17.6

[1] Includes non-cash asset retirement costs as follows: 2014Exploration costs$ -  -  -  -  -  - Development costs 36.5  (32.1) 66.2  -  -  70.6 $ 36.5  (32.1) 66.2  -  -  70.6 2013Exploration costs$ -  0.2  - -  -  0.2 Development costs 70.1  5.9  95.9  -  -  171.9 $ 70.1  6.1  95.9  -  -  172.1 2012Exploration costs$ (1.7) 0.1  - -  -  (1.6)Development costs 37.9  80.7  48.6  (11.5) 17.6  173.3 $ 36.2  80.8  48.6  (11.5) 17.6  171.7

[2] Includes property costs associated with non-cash capital lease of $358.0 million at the Kakap field.

[3] The Company has accounted for U.K. operations as discontinued operations due to the sale of these operations in the first half of 2013.

[4] Due to the shutdown of production operations in Republic of the Congo, the Company now includes the result of these operations in the Other exploration and production segment in the above table.